The gravitational path integral from an observer’s point of view

In this talk, we will discuss recent work attempting to develop a framework for describing non-perturbative gravitational physics relative to an observer. We apply our proposal to an observer that lives in a closed universe and one that falls behind a black hole horizon. We find that the Hilbert space that describes the experience of the observer is much larger than the Hilbert space in the absence of an observer. In the case of closed universes, the Hilbert space is not one-dimensional, as calculations in the absence of the observer suggest. Rather, its dimension scales exponentially with G^{-1}_N. Similarly, from an observer’s perspective, the dimension of the Hilbert space in a two-sided black hole is increased.